This invention relates to the formation of fibers from attenuable material and while the invention is adapted for use in the formation of fibers from a wide variety of attenuable matterials, it is particularly suited to the attenuation of various thermoplastic materials, especially mineral materials such as glass and similar compositions which are rendered molten by heating. As with the technique of the prior applications above referred to, the present invention may be employed in connection not only with various mineral materials, but also with certain organic materials which are attenuable, such as polystyrene, polypropylene, polycarbonate and polyamides. Since the equipment or apparatus is especially useful in the attenuation of glass and similar thermoplastic materials, the following description refers to the use of glass by way of illustration.
The above identified application Ser. No. 762,789, and also various other prior applications referred to disclose certain techniques for utilizing whirling currents or tornadoes for the attenuation of molten glass. In said application Ser. No. 762,789 the system for developing the secondary or carrier jets which penetrate into the principle current or blast involves the use of a series of jet orifices delivering gaseous jets against the surface of an inclined baffle or deflector, providing for deflection of the jets and for flow of the deflected jets in directions toward and penetrating the blast in order to develop "toration" zones, i.e. zones of interaction in the blast characterized by pairs of tornadoes in which attenuation of the glass streams is effected. In said prior application Ser. No. 762,789 the jets and the deflector are arranged so that the jets tend to spread laterally upon impingement thereof on the deflector surface, and the spacing of the jets is sufficiently close to provide for impingement of the jets upon each other near the free edge of the deflector surface. This impingement and the deflection of the jets results in development of pairs of whirling currents or tornadoes adjacent the edges of each jet, and further results in low pressure zones in each jet just downstream of the edge of the deflector, into which zones ambient gas or air is induced. In said low pressure zones the gas flow is substantially laminar, and the streams of molten glass are introduced into the system in said laminar flow zones, thereby providing stability of feed of the glass streams into the system. The glass streams are then advanced with the flow of each jet toward the zone of interaction produced by penetration of each jet into the blast, with consequent attenuation of the stream in said zones of interaction.
As in said application Ser. No. 762,789, the system of the present invention also provides for development of toration zones by penetration of jets into a blast and for attenuation of streams of molten glass in said zones, but in the system of the present invention the jets are developed in a different manner, and feed of the streams of molten glass is differently oriented with relation to the jets, than in the Ser. No. 762,789 application referred to.
In the system of the present invention, provision is made for generation of a plurality of jets with their axes lying in spaced side-by-side planes, which planes are referred to herein as the median planes of the jets. Perpendicular to the median planes, the axes of the jets initially lie in a common plane which is tangent to a convexly curved surface of a guiding device, so that the jets are subjected to a Coanda effect causing jets to deflect and follow the curvature of the convexly curved surface of the guiding device.
The jets are delivered from orifices which are preferably of greater cross sectional dimension in the common plane in which the jets are initially generated, as compared to the cross sectional dimension perpendicular to said common plane.
With the arrangement of the jets and jet orifices just described, the deflection of the Coanda deflection of the jets results in development of a pair of whirling currents or tornadoes within the flow of each jet, and the direction of turning of these currents and the interspacing between the jets results in induction of ambient gas or air adjacent to the surface of the curved guiding element in the spaces between the jets. This induced flow over the surface of the curved guiding element between the jets represents a substantially laminar flow, and the streams of molten glass are introduced into this laminar flow between adjoining jets.
Feed of the glass streams into the laminar flow zones intermediate the jets in the region of the surface of the curved guiding element increases the stability of feed of the glass streams. In a manner more fully explained hereinafter, each stream of molten glass is then drawn from the zone of laminar flow into the flow of one of the jets and is carried thereby into the zone of interaction with the blast, for attenuation therein. The feed of the glass into the jet system also effects preliminary attenuation of the glass stream, as will also be explained.
Notwithstanding the fact that the glass streams are fed into the influence of the jets in planes intermediate to the median planes of the jets, a high degree of stability of feed is provided because the zones of laminar flow into which the streams are delivered are located on the surface of the curved guiding element, which is a fixed structural part.